The present invention relates to a bidirectional communication system and a calibrator. More particularly, the invention relates to a two-wire bidirectional data communication system including a data line for transferring data signals and a clock line for transferring clock signals, in which plural stations having common pull-up resistances are provided, and to a calibrator.
The background of the invention will be described with reference to FIG. 1. Here FIG. 1 is a block diagram of a two-wire bidirectional data communication system. In FIG. 1, a data line 12 and a clock line 13 include a pull-up resistance 14-1 and a pull-up resistance 14-2 respectively to which a master station 11-1 and plural slave stations 11-2 to 11-N are connected.
The master station 11-1 includes a field-effect transistor (FET) 24-1 for generating data output and an amplifier 22-1 for performing data input in order to input and output data signals, each of which is connected to a data unit 23-1 for performing signal processing of transmitted data and received data. Also there are connected a field-effect transistor 27-1, an amplifier 25-1, and a clock unit 26-1 in the similar way for clock signals.
The slave stations 11-2 to 11-N have the same configuration as the master station.
In this system, the data line 12 of the master station 11-1 and slave stations 11-2 to 11-N is connected to the pull-up resistance 14-1. Also the clock line 13 thereof is connected to the pull-up resistance 14-2. Further, due to wiring, a parasitic capacitance 21-1 is generated between an earth potential and the data line 12, and a parasitic capacitance 21-2 is generated between an earth potential and the clock line 13.
The two-wire bidirectional data communication system is disclosed in U.S. Pat. No. 4,689,740. Incidentally JP-A No. 106262/1982 is the Japanese counterpart of U.S. Pat. No. 4,689,740.
In such a communication system having plural salve stations, the voltage levels of the data signal and clock signal as well as the timing characteristics, such as rise time and fall time, are dependent on the number of stations to be connected. For this reason, the connectable number of stations and the pull-up resistance value have been set in advance in consideration of the leakage current and the parasitic capacitance in each station.
Meanwhile in a system where the number of stations can be flexibly changed, the number of stations is changed in an application, so that the leakage current and the parasitic capacitance in each station are different from the design values. This has sometimes caused degradation of data signal waveform due to reduction of signal amplitude, increase of rise/fall time and the like.
There is described in U.S. Pat. No. 6,643,787 a method for suppressing communication errors caused by the signal degradation as described above. This technology includes a circuit called a data history generator in each slave station to optimize a bandwidth compensation circuit provided in a data receiving section so that each slave station suppresses the error rate of received data.
However, in the technology described in U.S. Pat. No. 6,643,787, complex circuits such as the data history generator and the bandwidth compensation circuit are necessary.